Heretofore, gear grinding machines are provided to efficiently finish the tooth surfaces of a workpiece, which is a heat-treated gear to be machined, by grinding the workpiece with a grinding wheel, which is a grinding tool. In such a gear grinding machine, the workpiece is ground in a state in which the grinding wheel and the workpiece are being rotated in synchronization while meshing with each other. Accordingly, insufficient precision of meshing may cause uneven grinding on the tooth surfaces of the workpiece and may reduce the life of the grinding wheel due to an excessive load thereon.
For the above-described reasons, in a gear grinding machine of this type, phasing is performed ahead of meshing at the time of grinding in order to mesh a grinding wheel with a workpiece with high precision. In the phasing, the grinding wheel and the workpiece are positioned so that the cutting edges (peaks and valleys) of the grinding wheel and the roots (peaks and valleys) of the teeth of the workpiece have an appropriate phase relationship. Such a phasing method for phasing a grinding wheel with a workpiece is disclosed in, for example, Patent Document 1.